Shakespeare invented many new English words. Over 1,500, in fact. “Epileptic” is one. “Puking” is another. “Alligator,” “skim milk” and “obscene” are a few more. In Act III of “A Midsummer Night’s Dream,” Oberon says to Puck:

“Then crush this herb into Lysander’s eye;Whose liquor hath this virtuous property,To take from thence all error with his might,And make his eyeballs roll with wonted sight.”

Before this speech there was “eye” and there were “balls” − but no one had thought to put them together. And that, it turns out, is a pretty big deal. Why? Well, if you’ve ever wondered why your eyeballs are so white − actually, the technical term for the white around the iris is the sclera − it turns out you’ve contemplated something very basic about what makes us who we are.

We’re the only primate with white sclerae, not to mention eyelids that allow our eyes to be clearly visible. Compared with the dark sclerae, the dark surrounding skin and droopy eyelids of chimpanzees, gorillas, bonobos and orangutans, our eyes render us open books.

Whether our heads lean left or forward, bob incessantly or stay as still as a church mouse, it’s easy to follow our gaze. This means that we can communicate better by signaling our intentions. And in allowing us to understand each other better, to read each other with ever increasing accuracy, our white eyeballs played a part in making us human.

If a white sclera provided an advantage in communication, a new theory now claims that our whites were not aimed exclusively at ourselves. Before we come to that, though, we need to consider a different question: How is it that we modern humans, Homo sapiens, survived and populated the planet, whereas Neanderthal man (Homo neanderthalensis) disappeared? After all, the Neanderthals had been successfully living in what is today Europe and parts of western and central Asia for well over 250,000 years before we showed up, walking out of Africa just 70,000 years ago. They made tools and created art, built homes with animal bones, even had a language.

As archaeological and paleontological evidence suggests, the two human species lived side by side in Europe and the Middle East for about 10,000 years, between 45,000 and 35,000 years ago. But then, rather suddenly, the Neanderthals began to dwindle. Whether or not there was a small amount of interbreeding between the two groups ‏(a matter that continues to be debated‏) more recently than 25,000 years ago, no Neanderthals remained.

What happened? The answer is that nobody really knows. Sudden climate changes that affected our stocky, large-headed cousins more than us − this is one hypothesis that’s been offered to solve the mystery. Two volcanic super-eruptions around 40,000 years ago is another. And violent extinction at our own hands is − albeit not terribly complimentary to ourselves − a third.

But now a new hypothesis has appeared, one that is not perhaps so damning as much as it makes us look rather differently at our canine companions. According to this theory, the reason why we humans made it through the Paleolithic era whereas Neanderthals whimpered and withered is that we domesticated dogs. Dogs are furry and cute, you might say, fun to play with, and really the sweetest little creatures. What kind of an advantage could they have possibly given us over the well-adapted, sturdier Neanderthal?

Paleolithic dogs weighed, on average, 32 kilograms and had a shoulder height of at least 60 centimeters. These were beasts comparable to today’s German Shepherds, not minuscule Pomeranians held on laps by petite models on the Champs Elysées.

At the sites where the canines’ remains were found in latter-day Siberia and the Czech Republic, an abundance of mammoth bones were also found. If the modern Blackfeet and Hidasta Indians of the American West – who used dogs as beasts of burden to lug their loads – are an example, it may well be the case that Paleolithic dogs helped carry mammoth meat from kill sites back to camp. If they did, they would have saved humans a lot of energy, rendering each kill a greater net gain in food. More food would mean better-fed mothers with more milk to service more babies. Which would mean population growth.

A recent paper in the Science journal by Paul Mellars and Jennifer C. French, analyzing 164 archaeological sites of Homo sapiens and Neanderthals, shows that in the period of overlap, we humans overwhelmed our cousins in sheer numbers, outbreeding them as much as 10 to 1. Could dogs lugging meat have been responsible?

All hypotheses about the deep past necessarily have to be tentative; there is a large element of storytelling just by dint of the métier. Alas, great swaths of our history will forever remain beyond our reach. But “Just So Stories,” à la Rudyard Kipling, can be convincing, which is why researchers have begun looking more closely at other ways dogs could have been helpful to humans.

Investigating the closest thing we have today to a mammoth hunt, a pair of researchers from the Finnish Game and Fisheries Institute compared the results of hunting moose with and without dogs, and found that using large Norwegian Elkhounds or Finnish Spitzes increased the average carcass weight per hunter by 56 percent. A further study of the Mayanga and Miskito peoples of Nicaragua showed that 85 percent of the mammals caught in hunts involved the use of dogs. In fact, dogs proved crucial for encountering game in the first place – the hunters were six times more likely to find armadillos using dogs, and nine times more likely to find agoutis ‏(large, and apparently very tasty, rats‏).

Dogs also save humans a lot of time. A recent study of the Bofi and Aka forest hunters of the Central African Republic showed that porcupine hunts were 57 percent faster, and pouched rat hunts 41 percent faster, when dogs were on the trail. These dogs were not cuddled or played with, but strictly used for hunting. The very idea that they should be thought of as pets or companions would be considered a joke and absurd.

Until recently, the domestication of dogs was thought to have occurred about 17,000 years ago, well after the last Neanderthal had perished. But archaeological finds in Belgium and elsewhere suggest that wild wolves may have been selectively bred by humans beginning as far back as twice that number of years. This would, more or less, coincide with the human-Neanderthal overlap, and yet all dog bones found so far have been exclusively in Homo sapiens sites.

In one of these, at Gravettian Predmostí in the Czech Republic, a complete skull of a dog was found with a large bone inserted between its jaw and cranium, suggesting that perhaps valued hunting dogs were honored and maybe even buried with ritual.

Which brings us back to Shakespeare and eyeballs. In “A Midsummer Night’s Dream,” Lysander falls in love with Hermia, but cannot marry her because her father wants her to wed Demetrius. Running away on a forest path together, the lovers − and Demetrius − encounter the mischievous elf Puck, who applies a magic ointment to the eyes of the two men, making them both fall in love with a second woman, Helena. Poor Hermia is dismayed, but not all is lost. Puck applies the ointment again, this time only to Lysander, whose love for Hermia is magically restored. Since Demetrius remains in love with Helena, the two couples can live happily ever after − all’s well that ends well.

“The course of true love never did run smooth,” Lysander comforts his beloved, expressing the theme of the play. But another way to look at it is that eyes matter.

What, then, is the connection between humans and Neanderthals, eyeballs and dogs? In a recent article in American Scientist, anthropologist Pat Shipman tenders a guess. In the years that the great British primatologist Jane Goodall lived at Gombe Stream National Park in Tanzania, she observed two male monkeys with a mutation: Their sclera were white. A third female developed white sclera in old age. But the mutation didn’t spread, and died with the monkeys.

Why? Shipman suggests the answer might have to do with the fact that while chimps do hunt, meat makes up only 2 percent of their diet. Paleolithic humans, on the other hand, depended on game to a much greater extent (closer to 30 percent). Since being able to read a gaze is of great help in communicating during a silent hunt, clear sclera would stand to benefit early humans handsomely but carry less advantage for chimpanzees. And the whiter our sclera, the better overall cooperators we could become.

If white eyeballs played a role in turning us into the über-cooperative species that we are, they might also explain why dogs provided such an advantage. For dogs are notoriously good at following eyes: as good, in fact, as human infants. When you move your head but keep you eyeballs still, dogs, unlike monkeys, are not fooled. That we, rather than Neanderthals, should have domesticated dogs may provide a new and fascinating piece for solving the puzzle of their disappearance and our triumph. And, of course, this might be part of the explanation of our white eyeballs. Man’s best friend indeed, but also his maker.

Still, notice how many assumptions go into this theory: 1‏) That dogs make hunts more efficient because they take cues from human gazes; 2‏) That human sclera were not white, or as white, before the domestication of dogs; 3‏) That selection pressures for coevolution of white sclera and dog hunting were strong enough compared to selection pressures for white sclera to aid communication in humans alone; 4‏) That a greater mutation rate for white sclera in humans allowed our early ancestors, and not Neanderthals, to put especially tame wolves or “incipient dogs” on the hunt; 5‏) That the canine bones found in early archaeological sites belonged to hunting dogs; and 6‏) That we did in fact domesticate dogs as early as 40,000 years ago. The list goes on and on. Not one of these assumptions is proven.

At the moment, then, this is nothing more than, if you like, a midsummer night’s dream. So hold your applause and keep your eyes open for new evidence. The course of finding the truth, after all, as Shakespeare and his heroine Hermia knew all too well, never did run smooth.

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